Thin film metal non-oxide coated substrates

ABSTRACT

Three dimensional inorganic powder substrates, with shielded surfaces, having metal non-oxide-containing coatings are disclosed. The coated substrates are produced by the process comprising reacting a powder particle substrate with a metal non-oxide and anion forming precursor reactant mixture at fast reaction and elevated temperature reaction conditions to form a substrate containing metal non-oxide on at least a portion of the three dimensions and shielded surfaces of the substrate. The coated substrates are useful in polymers, catalysis, heating and shielding applications.

BACKGROUND OF THE INVENTION

The present invention relates to a process for coating powder particlesubstrates, the coated powder particle substrates and to applicationsand uses thereof. More particularly, the invention relates to coatingpowder particle substrates with a metal non-oxide-containing material,such material preferably being an electrically and/or thermallyconductive non-oxide-containing material and such coated powdersubstrates.

In many applications using powder it would be advantageous to have anelectrically and/or thermally conductive; radiation absorbing and/oranti friction metal non-oxide coatings which are substantially uniform,have high and/or designed conductivity and/or radiation absorbingproperties and have good chemical properties, e.g., morphology,stability, corrosion resistance, etc.

A number of techniques have been employed to provide certain metalnon-oxide coatings on fixed generally larger size substrates. Forexample, the CVD processes are well known in the art for coating asingle flat surface, which is maintained in a fixed position during thecontacting step. The conventional CVD process is an example of a“line-of-sight” process or a “two dimensional” process in which themetal non-oxide is formed only on that portion of the substrate directlyin the path of the metal source as metal non-oxide is formed on thesubstrate. Portions of the substrate, particularly internal and externalsurfaces, which are shielded from the metal non-oxide being formed,e.g., such as the opposite side and edges of the substrate which extendinwardly from the external surface and substrate layers which areinternal or at least partially shielded from the depositing metalnon-oxide source by one or more other layers or surfaces closer to theexternal substrate surface being coated, do not get uniformly coated, ifat all, in a “line-of-sight” process. Such shielded substrate portionseither are not being contacted by the metal source during line-of-sightprocessing or are being contacted, if at all, not uniformly by the metalsource during line-of-sight processing. A particular problem with“line-of-sight” processes is the need to maintain a fixed distancebetween the source and the substrate. Otherwise, metal non-oxide can bedeposited or formed off the substrate and lost, with a correspondingloss in process and reagent efficiency.

There has been a need to develop processes for producing metal non-oxidecoated powder substrate particles and processes, particularly under fastreaction processing conditions, which provide short processing timesrequired for producing high quantities of metal non-oxide coated powderparticle substrates and to produce unique metal non-oxide coated powdersubstrates having improved properties

BRIEF SUMMARY OF THE INVENTION

A new process, e.g., a “non-line-of-sight” or “three dimensional”process, useful for coating of three dimensional powder particlesubstrates has been discovered. As used herein, a “non-line-of-sight” or“three dimensional” process is a process which coats surfaces of apowder substrate with a metal non-oxide coating which surfaces would notbe directly exposed to metal non-oxide-forming compounds being depositedon the external surface of the substrate during the first line-of-sightcontacting step. In other words, a “three dimensional” process coatscoatable powder substrate surfaces which are at least partially shieldedby other portions of the powder substrate which are closer to theexternal surface of the powder substrate and/or which are further fromthe metal non-oxide forming source during processing, e.g., the internaland/or opposite side surfaces of for example glass, ceramic or mineralpowder particle substrates such as fibers, spheres, flakes or othershapes or surfaces including porous shapes.

A new fast reaction, elevated temperature process for coating a threedimensional powder substrate having shielded surfaces with a metalnon-oxide, preferably a conductive or absorbing metal non-oxide coatingon at least a part of all three dimensions thereof and on at least apart of said shielded surfaces thereof has been discovered. In brief,the process comprises forming a reaction mixture comprising powdersubstrate particles, a metal non-oxide precursor, for example, silicon,aluminum, boron and titanium precursors, such as partial oxide andchloride containing precursors and an anion forming precursor preferablyat least the powder substrate particles and metal non-oxide precursorbeing in a liquid form and/or in a flowable powder form said metal andthe anion of the precursor being chemically different and reacting thereactant mixture under fast reaction short residence time, hightemperature reducing conditions in a reaction zone to form a metalnon-oxide coated substrate and recovering such coated substrate,preferably a conductive or radiation absorbing non-oxide-containingcoated substrate.

The anion forming precursor is typically a precursor agent that providesthe non-oxide portion of the metal such as boron, nitrogen, silicon,carbon and sulfur. The anion forming precursors can be in the form of agas, liquid or solid for example methane and carbon powder as a sourcefor carbon, nitrogen and ammonia as a source for nitrogen, boron halidessuch as boron trichloride as a source for boron, sulfur halides andhydrogen sulfide as a source for sulfur and various silicon halides andhydrosilicides as a source for silica.

The forming of the metal non-oxide precursor/substrate and anion formingprecursor reactant mixture preferably takes place closely in time toreacting in the reaction zone. In a particularly preferred embodiment,the reaction mixture after formation is introduced directly into thehigh temperature reaction zone under fast reaction processing reducingconditions. The coated powder substrate is then recovered byconventional means.

The process can provide unique coated substrates including single andmixed non-oxides which have application designed conductivity and/orabsorbing properties and/or anti friction lubricant properties so as tobe suitable for use as components such as additives in a wide variety ofapplications. Substantial coating uniformity, e.g., in the thickness ofthe metal non-oxide coating is obtained. Further, the present metalnon-oxide coated substrates in general have outstanding stability, e.g.,in terms of electrical or thermal properties and morphology and are thususeful in various applications.

DETAILED DESCRIPTION OF THE INVENTION

The present coating process comprises forming a reactant mixture of apowder substrate, a metal non-oxide precursor, such as metal partialoxide and/or chloride forming components, metal complexes and mixturesthereof an anion forming precursor and reacting the reactant mixture, atfast reaction, elevated temperature process conditions, preferablyreducing conditions, effective to form a metal non-oxide containingcoating on the powder substrate. The components of the reactant mixtureare reacted at conditions effective to convert the metal non-oxideprecursor to metal non-oxide and form a metal non-oxide-containingcoating, preferably a conductive, or radiation absorbing metalnon-oxide-containing coating, on at least a portion of the substrate.The process as set forth below will be described in many instances withreference to various compounds of silica, titanium, aluminum and boronwhich have been found to provide particularly outstanding process andproduct properties. However, it is to be understood that other suitablemetal non-oxide precursors are included within the scope of the presentinvention.

As set forth above the reactant mixture is subjected to reducing fastreaction processing conditions at elevated temperatures in order to forma metal non-oxide coating on the substrate. The reactant mixturepreferably should be formed prior to high temperature fast reactionprocessing conditions. This reduces metal non-oxide precursor formingoff of the substrate which decreases the yield of metal non-oxide coatedsubstrate. By “forming” is meant that the metal non-oxide precursor ispreferably associated with the powder substrate before deleteriousreaction of the metal non-oxide precursor with the anion formingprecursor can take place off the substrate, such as not to be associatedwith the substrate as a powder coating. It has been found that thepreferred reactant mixtures are those that are formed proximate in timeto the introduction of the reactant mixture into the high temperaturefast reaction zone. Thus for example, the reactant mixture can be aliquid slurry wherein the metal non-oxide precursor is soluble in theliquid and/or an insoluble solid in the liquid slurry. Further, theliquid slurry can be a suspension of the metal non-oxide precursor. Theprecursor preferably is a precipitate on the substrate in the liquidsolid slurry. Further the reactant mixture can be a solid or flowablepowder form such as a precursor powder and/or precipitate and/or liquidfilm coating of metal non-oxide precursor. Each of the above reactantmixtures can offer unique and distinct processing product advantages inthe process of this invention. The liquid slurry reactant mixtures arepreferably atomized, such as gas atomized, upon introduction with thesubstrate into the reaction zone for conversion to the metal non-oxidecoated substrates. Further, the flowable powder reactant mixtures suchas precursor powder, precipitate and liquid film reactant mixtures, canbe air fluidized into the reaction zone or gravity or mechanically fedinto the reaction zone. For liquid reactant mixtures, it is preferred tomaximize the concentration of the substrate in the liquid slurries on awt % basis so as to maximize the association of the metal non-oxideprecursor with the substrate. It is preferred that the concentration ofsubstrate in liquid slurries be from about 10 to 65 wt % more preferablyfrom about 30 to 60 wt % or higher. As is recognized by those of skillin the art, the viscosity of the slurries will vary as a function of theparticle size, its geometry and density. Viscosities are used whichallow for overall optimum process efficiencies on a product quality andthroughput basis.

The anion forming precursor can be a gas, liquid or a solid. As setforth above the anion forming precursor can be a gas such as methane,chloro methanes and ethanes, nitrogen, ammonia, boron trichloride,hydrogen sulfide and the like. The anion forming precursor associateswith the metal non-oxide precursor/substrate at and during the reactionsin the reaction zone. For example the anion forming precursor in theform of a gas can be at least a part of the carrier gas used to atomizeand/or fluidized the substrate metal non-oxide precursor. Further, theanion precursor gas can be introduced into the reaction zone with themetal oxide precursor substrate such that reaction takes place for theconversion to metal non-oxide coating on the substrate. In addition theanion forming precursor can be in the form of a solid such as a powderwhich is also associated with the substrate similar to or the same asthe metal non-oxide precursor. As set forth above, there is an intimateassociation of the metal non-oxide and anion forming precursors in orderfor fast reaction conversion to the metal oxide coating on the substrateto occur at the short residence time, high temperature conditions in thereaction zone.

The fast reaction processing conditions as set forth above include avery short reaction residence time for the powder particles in theelevated temperature reaction zone. “Reaction zone” is defined as thatzone at elevated temperature wherein fast reaction of the metalnon-oxide precursor with the anion forming precursor takes place on thesubstrate such that the metal non-oxide precursor is not substantiallylost as separate metal non-oxide particles not associated with thesubstrate. Thus the reaction zone allows for association of the metalnon-oxide precursor on the substrate wherein subsequent processing willnot substantially adversely affect the overall metal non-oxide coatingon the substrate. It is important that the residence time in theelevated temperature reaction zone associate the metal non-oxideprecursor with the substrate. It is contemplated within the scope ofthis invention that further processing such as conditions to promotefurther reduction, uniform crystallinity and/or coating densificationcan be carried out according to the process of this invention.

The fast reaction processing conditions in the reaction zone can vary asto temperature and residence time according to the physical and chemicalproperties of the metal non-oxide precursor and substrate. The averageparticle residence time in the reaction zone is less than about onesecond preferably from about 0.5 milliseconds to about 1 second, morepreferably from about 1 millisecond to about 500 milliseconds and stillmore preferably from about 5 milliseconds to about 250 milliseconds.Further, the residence time can be defined by the particle velocity inthe reaction zone. Preferably the average particle velocity in thereaction zone is from about three to about 30 meters/second, morepreferably from about three to about 10 meters/second.

The elevated temperature in the reaction zone is maintained by a thermalsource that rapidly transfers thermal energy to the reactant mixture.The unique combination of reactant mixture, short residence time and athermal source for rapid thermal transfer provides for rapid associationof the metal non-oxide precursor with the substrate on both external andshielded surfaces without substantially adversely effecting the solidintegrity of the substrate. By the term solid integrity is meant thatthe substrate retains at least a part preferably a majority an even morepreferably a substantial majority of the substrate as a solid under thetemperature conditions in the reaction zone. Depending on the physicaland chemical properties of the substrate the surface and near surface ofthe substrate can become reactive and/or melt under the thermalconditions in the reaction zones. The highly reactive surface and/orrapid melting and solidification for certain substrates can provideenhanced properties associated with the metal non-oxide coating such asbarrier properties, binding properties and preferential crystallinesurface formation by the substrate. The short residence times in thereaction zones allow for rapid chemical reactions and rapid quench whenthe substrate particles leave the reaction zone.

One of the unique advances of the process of this invention is theformation of very thin metal non-oxide coatings on powder substrateswithout substantially adversely affecting the solid integrity of thesubstrate, i.e. the inner core of the substrate is essentiallychemically unaltered. Thus, the metal oxide precursor associated with orformed from the substrate as a thin film and/or the outer surface of thesubstrate has a reactive surface which exhibits high reactivity as aprecursor and provides for the formation of the metal non-oxide coatingunder fast reaction processing conditions. Thus, only the thin filmmetal oxide precursor and/or reactive surface on the substrate have tobe converted via reaction with the anion forming precursor. As set forthabove, the substrate retains an inner core of essentially the samechemical composition as the original starting substrate. Thus, in thepreferred embodiment of this invention, the metal non-oxide precursorcan be for example a preassociated flowable powder, i.e. a precoat of apowder, precipitate or film forming liquid or the surface itself of thesubstrate where thin film reaction with the anion forming precursortakes place in the reaction zone. Typical examples of substrate surfacereaction is carboreduction and nitriding of aluminum, boron and silicaoxides or particle oxides.

The thermal source produces elevated temperatures that allow for thereactant mixture to rapidly produce metal non-oxide coated substratesand allows residence times that provide for the association of the metalnon-oxide precursor with the substrate and reaction with the anionforming precursor. Thus the thermal source must allow for control of theelevated temperature to produce metal non-oxide coated substrates and aresidence time which allows the chemical reactions and/or association ofthe metal non-oxide precursor with the substrate to take place on thesubstrate. The preferred thermal sources which allow for control ofelevated temperatures and the residence times necessary for chemicalreaction and/or association of the metal non-oxide precursor with thesubstrate are induction plasma sources preferably RF induction plasmasources and flame combustion sources.

As set forth above, the thermal source provides an elevated temperaturethat primarily acts on the metal non-oxide precursors and anion formingprecursor such that the powder substrate, primarily the internalportions of the substrate are at a lower temperature than the externaltemperature in the reaction zone. As will be more fully described below,the typical substrate can have a relatively low heat transfercoefficient which when combined with the short residence times in thereactions zone allows for such differential between the externaltemperature and the internal temperature of the substrate. Further theprocessing conditions can be adjusted to take advantage of this thermalgradient particularly as to selective reaction of the anion formingprecursor on the surface, melting and resolidification andcrystallization on the surface and near surface of the substrate.Further, the temperature within the reaction zone is controlled to allowrapid reaction of the metal non-oxide precursors and anion formingprecursor which reactions can increase substantially the association ofthe coating and yields, i.e. reduced tendency towards volatilization andfurther the completion of the overall reaction to metal non-oxidecoating. As set forth above, one of the major advances is theassociation of the metal non-oxide precursor coating through thereaction zone into the quench stage. The recovered metal non-oxidecoated substrates can be further annealed for further densification,crystallization and minimizing the presence of deleterious amounts ofcontaminants such as oxygen.

RF inductively coupled plasma systems are well known to those ofordinary skill in the art and typically consist of an RF power generatorsupplying a RF current to an induction coil wound around a plasmaconfinement tube. The tube confines the plasma discharge. Power levelsfor plasma systems can vary from about 10 kW up to about 500 kW. Typicalfrequencies vary from about 0.3 MHz to even as high as 14 MHz. Typicalranges are in the 0.3 to 5 range.

The plasma system typically uses three different gases including acentral gas sometimes referred to as a central swirl gas used primarilyfor formation of the plasma, a sheath gas used primarily to stabilizeand center the plasma and a third carrier gas which typically is used totransport a powder feed and/or atomize a liquid slurry feed. As isrecognized by those of ordinary skill in the art, the composition of allthree gases can vary and can include gases such as argon, nitrogen,hydrogen as well as other gases such as anion forming precursor gases.In addition mixtures of varying gases can be used depending on thecharacteristics of the plasma that is required for the process. As setforth above, a component of the plasma gases can serve as an anionforming precursor and a reducing agent. In other cases, a secondary gascan be injected into the plasma or sheath surrounding the plasma toprovide the anion forming precursor. The gases used as sheath, centraland carrier gases can be different or the same and mixtures of differentgases can be used. For example, a reducing gas can be used for thesheath, central and carrier gas or various other gases, such as argon,can be combined with the sheath or central gas. The gas flow rates forthe central, sheath and carrier gases can vary over a wide range withsuch ranges being adjusted to within the residence time and particlevelocities required for the conversion of the metal non-oxide precursorto coated metal non-oxide substrate. In general the rate of introductionof the sheath, central and carrier gases will vary with typically thesheath gas being introduced at a rate of from about three to about fivetimes that of the central swirl gas. In addition, the central swirl gasrate will generally be higher than the carrier gas since the carrier gasis used to control the rate at which the reactant mixture is introducedinto the reaction zone. The gas compositions and flow rates can beoptimized to provide desired process conditions. For example, nitrogencan be introduced into the central gas in order to lower the overalltemperature profile within the reaction zone. Typically the other gasrates and/or partial pressure within the given gas composition arelowered in order to control the particle residence time and particlevelocities within the reaction zone. Further, the anion formingprecursor content in the various gases within the reaction zone can beadjusted to provide near stochiometric quantities or slight excess inorder to limit the amount present in the later portion and tail of thereaction zone. In addition, anion forming precursor enrichment can takeplace such as the introduction of anion forming precursor at the tail ofthe reaction zone to provide enhanced overall reaction conditions priorto quench. Typically, the enthalpy of the gas composition is controlledso as to maintain the elevated temperature that promotes rapid reactionof the metal non-oxide precursors with the anion forming precursor onthe substrate. Thus the enthalpy of components such as hydrogen andorganic components added as part of the liquid slurry and powderreaction mixtures are taken into consideration for defining thetemperature required in the reaction zone. Further, the gas rates(volume of gas per unit time) will vary depending on the size and designof the process equipment. As set forth above, the residence times arelong and the particle velocities slow when compared to typical sonic andsupersonic plasma type systems. As is set forth above, an anion formingprecursor and reducing conditions allow for the reaction of metalnon-oxide precursor to metal non-oxide coating on the substrate to takeplace within the reaction zone at elevated temperatures. It has beenfound that the residence times and/or particle velocities as set forthabove together with the control of gas composition and temperatureconditions allow for the reactions to take place on the substrate toproduce the metal non-oxide coated substrates. The control by thethermal source of the temperature in the plasma or adjacent to theplasma, i.e. reaction zone, allows for the reactions to take place whilenot substantially adversely effecting the solid integrity of thesubstrate. Further, the temperature and the dimension of the plasma canbe adjusted so as to provide selective reaction with the anion formingprecursor and/or melting on the surface or near surface of the substrateto enhance overall reaction, bonding and uniformity of the metalnon-oxide coating on the substrate. As set forth above, the temperature,particle residence time and anion forming precursor concentration allowfor the conversion of the metal non-oxide precursor to metal non-oxidecoating while not adversely effecting the solid integrity of thesubstrate. Thus, the temperature within the reaction zone can varyaccording to the above process conditions and typically are in the rangeof from about 1000° K. to about 4500° K., more preferably from about1500° K. to about 3500° K. As set forth above, the temperature can bemoderated by auxiliary gases including inert gases.

The reactant mixture can be introduced into the plasma at varyinglocations within the plasma including the tail, i.e. terminal, portionof the plasma flame. The reactant mixture in addition can be introducedlaterally into or adjacent to the plasma flame and/or the tail of theplasma flame or at varying angles to the plasma including perpendicularto the plasma or the plasma tail. In a typical system configuration aprobe of appropriate metallurgy such as inconel, is centrally mounted inthe plasma confinement tube. Typically a quartz tube is interposedbetween the probe and the confinement tube. The central gas in injectedinto the quartz tube and the sheath gas is injected in the annularpassage defined between the quartz tube and the plasma confinement tube.Conventional cooling of the system is used. The reactant mixture feedprobe can be used to gas atomize the liquid slurry reaction mixtures ofthis invention and/or gas atomize, such as with an inert and/or anionforming precursor gas and mixtures thereof, the powder feeds of thisinvention. For example, in the liquid slurries, fine droplets of theliquid slurries can be injected typically into the central portion of oradjacent to the plasma discharge. Further, the position of the injectionprobe within or adjacent to the plasma for powder or liquid slurries canbe varied such as to optimize the performance and overall yields ofmetal non-oxide coated substrates. As is set forth above, the reactionmixture can be introduced into the tail of the plasma discharge such aslaterally or at an angle into the plasma tail. It is preferred that thereactant mixtures from liquid slurries to powders be introduced into thereaction zone with a carrier gas, particularly an inert and/or reducingand anion forming precursor containing carrier gas and mixtures thereofwhich enhances the rate of reaction of the metal non-oxide precursor tometal non-oxide coating on the substrate. The powders can be gravity fedand/or continuously fed such as by screw feeders into the plasma. In apreferred embodiment of this invention, the concentration of thesubstrate in the liquid slurries can be maintained at a relatively highconcentration such as from 30 to 60-wt % or higher in order to optimizethe interaction between the metal non-oxide precursor and substrate. Theconcentration can be adjusted in order to maintain a liquid reactantmixture viscosity which enhances atomization of the liquid reactantmixture and overall steady state process and plasma conditions forconversion and yield of metal non-oxide coated substrate. Further, thereaction zone can be run at varying pressures including reducedpressures through higher pressures above atmospheric. The choice ofpressure is generally a function of the characteristics of the metalnon-oxide precursor and anion forming precursor. It is preferred tomaintain such conditions of pressure which improve the overallconversion and yield of metal non-oxide coating on the substrate whilereducing and/or minimizing the reaction of metal non-oxide precursor tometal non-oxide off of the substrate.

The feed rates of the liquid slurries and powders in general are afunction of the reaction zone design and size. In general for smallscale reaction zone designs a feed rate of from 100 grams to 500 gramsper hour can be used, whereas for larger scale, a feed rate of from 0.5Kg to 50 Kg per hour can be used.

The liquid slurries and flowable powder reactant mixtures can containvarious substantially nondeleterious materials including solvents, i.e.organonitrogen containing solvents for liquid slurries and organicpolymeric binders which may decrease or increase the elevatedtemperature or enthalpy in the reaction zone. The thermal contributionof these materials is used in order to design the thermal profile in thereaction zone in order to maximize steady state process conditions andconversion and yields of metal non-oxide coated substrate. Further, theuse of such materials, particularly, organic materials can be used toadjust the composition of the plasma gases as a function of the gascomposition from gas entry to exit from the reaction zone. For example,the hydrogen requirement for the reaction and reduction of the metalnon-oxide precursor to metal non-oxide coating can be adjusted such thata portion of the plasma and gas composition exiting the tail of theplasma can be in an overall reducing environment. The processflexibility in the introduction of varying gases of varyingcharacteristics allows such changes in gas composition as a function ofplasma profile and exit gases to be made. For example, in the use ofpartial oxide and metal chloride precursors it has been found that astaged reducing environment enhances overall conductivity of the metalnon-oxide film on the substrate. Further, the use of carbon dioxide suchas in very low oxygen containing gases from partial combustion ofhydrocarbon can be used advantageously to promote the formation of amultiple reduction zones within the reaction zones and/or a reductionzone following the exit of the plasma gas from the reaction zone.Further, it is possible to add auxiliary gases such as reducing gasesinto the plasma at different introduction points within the plasma.

The metal non-oxide coated substrates exit the reaction zone and arerapidly quenched to lower temperatures including temperatures whereinrelatively low, preferably no significant oxidation is taking place ofthe metal non-oxide coating. The metal non-oxide coated substrates arerecovered by conventional means such as typical powder particlecollection means. As set forth above, the metal non-oxide coatedsubstrates can be further processed such as by annealing to furtherdensify the metal non-oxide coatings and/or more fully develop theoptimum crystal structure for enhancing overall conductivity and/orabsorbing of the final coated substrate.

As set forth above, the thermal source can be obtained from combustionsuch as a flame produced by the combustion of a gas such as acetylene,methane or low molecular weight hydrocarbons, hydrogen and ammonia. Thethermal and kinetic energy associated with the combustion process can bevaried to provide elevated temperatures and residence times and/orparticle substrate velocity within the ranges as set: forth above atnon-stoichiometric flame or reducing gas conditions. The combustionflame process provides a reaction zone wherein the gas compositionwithin the reaction zone can be varied according to the gas combustioncharacteristics used to provide the reaction zone. Further, thecomposition of the gas can be varied according to the type of gas usedin the combustion process and the ratio of combustion gas to inert gasthat is used to produce a reducing flame. Thus the amount of residualoxygen, carbon dioxide and water vapor can be limited by varying thestoichiometry of the reactants, the type of fuel source and reducingconditions. Further, auxiliary gases can be added to moderate and modifythe combustion flame characteristics. In addition, such auxiliary gasesincluding inert gases can be added directly into the combustion flame oras a sheath, i.e. curtain or shroud, surrounding the combustion flame.Further, the reactant mixture can be introduced directly into thecombustion flame or as in the case of the RF induction plasma at varyingangles to the flame or on the outer or adjacent surface or tail of theflame. The temperature profiles within the combustion flame aretypically lower than the temperatures that can be achieved in the RFinduction plasma typically in the range of from about 750° K. to about1,500° K. The unexpected process improvement for producing metalnon-oxide coated substrates with the combustion process is the formationof a reaction zone at temperatures and residence times which allow forthe conversion of the metal non-oxide precursor on the substrate to thecoating. The various embodiments set forth above with respect toreaction mixture introduction into the reaction zone, preference foratomization of the reaction mixtures, variations on introduction of thereaction mixtures at various locations within the reaction zone or atthe tail end of the reaction zone, variations in gas composition such asreducing zones are applicable to the combustion processes.

The thickness of the metal non-oxide-containing coating can vary over awide range and optimized for a given application and is generally in therange of from about 0.01 to about 0.75 microns or even from about 0.01to about 0.5 microns, more preferably from about 0.02 microns to about0.25 microns, still more preferably from about 0.02 microns to about 0.1micron.

The reactant mixture may also include one or more other materials, e.g.,dopants, catalysts, grain growth inhibitors, binders, solvents, etc.,which do not substantially adversely affect the properties of the finalproduct, such as by leaving a detrimental residue or contaminant in thefinal product after formation of the metal non-oxide-containing coating.Thus, it has been found to be important, e.g., to obtaining a metalnon-oxide coating with good structural, mechanical and/or electronicand/or magnetic properties, that undue deleterious contamination of thecoating be avoided. Examples of useful other materials include organiccomponents such as organic nitrogen solvents, such as acetonitrile,dichloro acetonitrile, pyridene, chloropyridene pyrrole and mixturesthereof; certain halogenated hydrocarbons, particularly chloro andmixtures thereof. Certain of these other materials may often beconsidered as a carrier, e.g., solvent, and/or anion forming precursorfor the metal non-oxide precursor to be associated with the substrate toform the reactant mixture.

The metal non-oxide coatings are typically derived from transition metalprecursors, which contain transition elements and Group III and Group IVmetals. Examples of such metals are boron, aluminum, silica, tin,nickel, chromium, tungsten, titanium, molybdenum and zirconium. Thepreferred elements are aluminum, boron, silica, tungsten, titanium,molybdenum and zirconium.

As set forth above the metal non-oxide precursor is preferably selectedfrom the group consisting of one or more metal chlorides, metal partialoxides, oxide organic complexes and organic salts. Further, it ispreferred that metal chlorides, organic complexes and salts and oxidesdo not allow substantially deleterious residual oxygen forming anion toremain in the coating under the conditions of conversion to metalnon-oxide in the reaction zone. Particularly preferred metal non-oxideprecursors are metal chlorides and lower valence organic nitrogencomplexes.

Typical examples of metal chloride precursors are nickel chloride,lanthanum chloride, zirconium chloride, aluminum chloride, ferricchloride, tungsten pentachloride, tungsten hexa chloride, molybdenumpentachloride, indium dichloride, indium monochloride, chromium²chloride and titanium tetrachloride. Preferred metal complexes arepolyfunctional nitrogen complexes wherein such functionality is capableof complexing with the metal. Typical examples of oxides are silica,boron oxide and boric acid.

Typical examples of anion forming precursors that produce borides areboron trichloride, borazine, diborane, and triethoxy boron; that producenitrides are nitrogen and ammonia; that produce suicides are silanes:and hydrosilicides; that produce carbides are methane, powdered carbon,low molecular weight halogenated hydrocarbons particularly chlorohydrocarbons, ethane and propane and that produce sulfides are hydrogensulfide and sulfur halides. In the practice of this invention, the anionforming precursor is selected for the final metal non-oxide coating tobe obtained, and anions not desired in the final coating should beavoided in the reactants and in the reaction zone.

The particular preferred coatings are silicon nitride, carbide andboride, aluminum nitride, zirconium carbide and silicide, tungstensulfide, boron carbide and nitride, titanium boride, carbide,carbonitride, silicide and nitride, molybdenum silicide and sulfide andiron silicide and nitride.

As set forth above, it has been found that the substrate can becontacted with a metal non-oxide precursor to form a flowable powderreactant mixture. For example, a metal non-oxide precursor can beapplied to the substrate as a powder, a precipitate and/or as a liquidfilm particularly at a thickness of from about 0.05 to about 1 micron,the thickness in part being a function of the substrate particle size,i.e. smaller substrate particles generally require even smaller sizeprecursors and thicknesses. The precursor can be applied dry to a drysubstrate and as a charged fluidized precursor, in particular having acharge opposite that of the substrate or at a temperature where theprecursor contacts and adheres to the substrate. In carrying out theprecursor coating, a coating system can be, for example, one or moreelectrostatic fluidized beds, spray systems having a fluidized chamber,and other means for applying for example powder, preferably in a filmforming amount. The amount of precursor used is generally based on thethickness of the desired metal non-oxide coating and incidental lossesthat may occur during processing. The process together with conversionto a metal non-oxide-containing coating can be repeated to achievedesired coating properties, such as desired gradient conductivities.

Typically, the fluidizing gaseous medium is selected to be compatiblewith the metal non-oxide precursor powder, i.e., to not substantiallyadversely affect the formation of a metal non-oxide coating on thesubstrate during conversion to a metal non-oxide-containing film.

Generally, gases such as nitrogen, argon, helium and the like, can beused, with nitrogen being a gas of choice, where no substantial adversereaction of the precursor takes place prior to the reaction to the metalnon-oxide coating. The gas flow rate for powder coating is typicallyselected to obtain fluidization and charge transfer to the powder. Finepowders require less gas flow for equivalent deposition. It has beenfound that very small amounts of water vapor can enhance chargetransfer. The temperature for contacting the substrate with a precursoris generally in the range of about 0° C. to about 100° C. or higher,more preferably about 20° C. to about 40° C., and still more preferablyabout ambient temperature. The substrate however, can be at temperaturesthe same as, higher or substantially higher than the powder.

The time for contacting the substrate with precursor is generally afunction of the substrate bulk density, thickness, precursor size andgas flow rate. The particular coating means is selected in partaccording to the above criteria, particularly the geometry of thesubstrate. For example, particles, spheres, flakes, short fibers andother similar substrate, can be coated directly in a fluidized bedthemselves with such substrates being in a fluidized motion or state.Typical contacting time can vary from seconds to minutes, preferably inthe range of about 1 second to about 120 seconds, more preferably about2 seconds to about 30 seconds.

Typical metal non-oxide precursor used for flowable reaction mixturesare those that are powder reaction mixtures at pre reaction zoneconditions and can be liquidous or solid at the fast reaction processconditions at the elevated temperatures in the reaction zone. It ispreferred that the precursor at least partially melt and substantiallywet the surface of the substrate, preferably having a low contact angleformed by the liquid precursor in contact with the substrate and has arelatively low vapor pressure at the fast reaction and temperatureconditions, preferably melting within the range of about 100° C. toabout 650° C. or higher. As set forth above, the fast reaction processconditions can allow for the metal non-oxide precursor to rapidly reactwith anion forming precursor to a highly viscous and/or intermediatesolid prior to substantial conversion to the metal non-oxide coating.The process conditions can allow for the association of thisintermediate metal non-oxide component to form and reduce thevolatilization and/or less of the metal non-oxide precursor off of thesubstrate.

As set forth above, the metal non-oxide precursors are preferablypreassociated with the substrate and gas fluidized into the reactionzone. It has been found that the preassociation of a thin coating ofmetal non-oxide precursor becomes highly reactive in the reaction zonethereby reducing and/or minimizing the loss of metal non-oxide precursorthrough volatilization. Examples of such association of metal non-oxideprecursor are fine powder coating of the substrate, precipitation of themetal oxide precursor on the substrate followed by drying such as spraydrying, the formation of a liquid film on the flowable powder substratesuch as by liquid droplets and conventional spray and dip coatingprocesses for preparing dry films on powder substrates. Thus, forexample an organic metal non-oxide precursor such as a titanate, asilane and/or other organic metal derivatives can be sprayed on thepowder substrate and dried and/or contacted through the use of anaqueous medium followed by drying such as spray drying.

As set forth above, the metal non-oxide precursor can be associated withthe substrate as a liquid slurry. For example, a liquid soluble metalchloride, i.e. chloride salt or a suspension and/or precipitatedsuspension, may be used. The use of liquid metal non-oxide precursorprovides advantageous substrate association particularly efficient anduniform association with the substrate. In addition, coating materiallosses are reduced.

The metal non-oxide precursors set forth above with respect to flowablepowders in general can be used also to make the liquid slurries. Inaddition, liquids, low melting and liquid soluble metal salts can beused advantageously for the liquid slurries.

As set forth above, it is preferred that the reaction mixture liquidslurries maximize the concentration of the substrate consistent withslurry viscosity and atomization requirements in the reaction zone. Theamount of metal non-oxide precursor which is incorporated into theslurry is generally a function of the thickness of the metal non-oxidecoating on the substrate for the final product. For example, a metalnon-oxide coating of 50 nanometers will typically require less than a150 nanometer metal non-oxide precursor coating. Further, the surfacearea of the substrate, typically a function of particle size per unitweight will effect the concentration of the metal non-oxide precursor.The reactant slurries can contain a solvent which allows for thesolubilization and/or precipitation of the metal non-oxide precursor.The preferred solvents are organic heteroatom solvent systems whichallow for solubilization of the metal non-oxide precursor and which donot contribute substantially deleterious anions to the desired coating.For example, a preferred liquid slurry which contains soluble metalnon-oxide precursor is titanium tetrachloride. The liquid slurries inaddition can have a pH higher or less than 7 which enhances overallsolubility and/or precipitation.

The precipitated liquid slurry reaction mixtures can be made by forminga first soluble solution of an appropriate metal non-oxide precursorsuch as metal chloride salts in a solution such as a basic solution andadding such solutions slowly at elevated temperature such as from about50° to 90° C. to a suspension of the substrate. The gradual addition ofthe metal non-oxide precursor solution generally in the presence ofsmall amounts of hydroxyl ion in the substrate suspension provides for aslow and gradual partial hydrolysis and precipitation of the salts,preferably on the surfaces of the substrate in a uniform layer. Theprecipitant slurry reactant mixture is introduced into the reaction zonefor conversion to the metal non-oxide coated substrate. One of thesignificant advantages of the process of this invention usingprecipitant slurry reaction mixtures is that the slurry itself can bedirectly fed into the reaction zone without requiring separation of theprecipitant plus substrate, washing of the substrate and drying of theprecipitant associated substrate. The precipitant slurry reactionmixture and the precipitant process are typically undertaken at highsubstrate liquid slurry concentrations without the introduction ofdeleterious contaminants. Thus it is preferred to use solvent systemswhich do not contribute deleterious contaminants to the metal non-oxidecoating. If a source of hydroxyl ion is used to enhance theprecipitation process it is preferred to use a source such as ammoniumhydroxide which does not substantially interfere with the finalproperties of the metal non-oxide film. Further, in the case ofprecipitant reaction mixtures, the precipitant substrates can befiltered, washed of extraneous ions and reslurried for use as a reactionmixture. In order to control the viscosity of the liquid slurries,particularly at high substrate concentration a dispersant or defloculantcan be added to reduce and/or minimize any substrate agglomeration.

The metal non-oxide precursor to be contacted with the substrate may bepresent in an atomized state. As used in this context, the term“atomized state” refers to both a substantially gaseous state and astate in which the metal non-oxide precursor is present as drops ordroplets and/or solid dispersion such as colloidal dispersion in forexample a carrier gas, i.e., an atomized state. Liquid state metalnon-oxide precursors may be utilized to generate such reaction mixture.

Any suitable means can be utilized to produce “the atomized state.” Aparticularly preferred atomized state is drops or droplets particularlyas a droplet dispersion. Typical examples of droplet and/or aerosolgenerators include nozzles and ultrasonic atomizing nozzles. Aparticularly preferred atomization technique is an ultrasonic atomizingnozzle since the nozzle produces a soft, low velocity spray, typicallyin the order of three to five inches per second. Further, droplet sizescan be varied over a wide range depending on the particle sizedistribution of the substrate. A particularly preferred ultrasonicatomizing nozzle is manufactured by Sono-Tek Inc. such as model8700-120. In a preferred process the ultrasonic generator produces afine mist having an average droplet size of about 18 microns or less.The droplets are contacted with a carrier gas, typically an inertcontaining gas such as argon or a reactive anion forming precursor gas.In a preferred embodiment the carrier gas contains the dispersedsubstrate which allows for substrate and droplet association. Thecontacting between the carrier gas dispersed substrate and the dropletsallow for a film forming amount of the droplets to become associatedwith at least a portion of the surfaces of the substrates. The substrateand droplets are typically maintained in a carrier gas fluidizedcondition which allows for association of the droplets with thesubstrates. Typically the contacting between the carrier gas substrateand droplets is at ambient temperature and for a period of time to allowfor the association of the droplets on the substrate surfaces. In orderto enhance contacting efficiencies a suitable apparatus such as a staticmixer can be used to accelerate the droplet substrate association. Thecontacting time between the carrier gas substrate and droplets under thecarrier gas fluidized conditions is typically less than twenty seconds,more typically less than ten seconds. In a preferred embodiment thedroplet associated substrate in a fluidized carrier gas is contacted atfast reaction and elevated temperature reducing conditions in a reactionzone in the presence of an anion forming precursor as set forth above.In a preferred embodiment the start of contacting under fast reactionconditions in the reaction zone is proximate in time to the associationof the droplets with the substrate, typically at a substrate filmreaction time after such substrate association of less than fiveseconds, more typically less than two seconds.

In a further preferred embodiment the metal non-oxide forming compoundis combined to form a liquid mixture prior to droplet formation. Thisallows for the metal non-oxide forming compound to be intimatelyassociated with the surfaces of the substrates. Further it is preferredthat the metal non-oxide forming compound has a higher reaction rate inthe reaction zone to metal non-oxide coating than the overallevaporation rate of the metal non-oxide forming compound. Thus, metalnon-oxide forming compound having boiling point above 100° C., morepreferably above 150° C. at atmospheric pressure is preferred.

In addition to the other materials, as noted above, the reactant mixturemay also include one or more grain growth inhibitor components. Suchinhibitor component or components are present in an amount effective toinhibit grain growth in the metal non-oxide-containing coating. Reducinggrain growth leads to beneficial coating properties, e.g., higherconductivity, more uniform morphology, and/or greater overall stability.Among useful grain growth inhibitor components are components whichinclude at least one metal ion, in particular potassium, calcium,magnesium, silicon, zinc and mixtures thereof. These components aretypically used at a concentration in the final coating of from about0.01 to 1.0 wt % basis coating. Of course, such grain growth inhibitorcomponents should have no substantial detrimental effect on the finalproduct.

The anion forming precursor may be deposited on the substrate separatelyfrom the metal non-oxide precursor, for example, before and/or duringthe metal non-oxide precursor/substrate contacting. If the anion formingprecursor component is deposited on the substrate separately from themetal non-oxide precursor it should be deposited after the metalnon-oxide precursor but before reaction to the metal non-oxide film.

Any suitable anion forming precursor may be employed in the presentprocess and should provide sufficient anion forming precursor so thatthe final metal non-oxide coating has the desired properties, e.g.,conductivity, stability, absorption properties, etc. Care should beexercised in choosing the anion forming precursor. For example, theanion forming precursor should be sufficiently compatible with, forexample, the metal non-oxide precursor so that the desired metalnon-oxide coating can be formed. Anion forming precursor which areexcessively volatile (relative to the metal non-oxide precursor), at theconditions employed in the present process, can be used since, forexample, the final coating can be sufficiently developed with thedesired properties even though an amount of the anion forming precursormay be lost during processing. It may be useful to include one or moreproperty altering components, e.g., boiling point depressants, in thereaction mixture. When used, such property altering component orcomponents are included in an amount effective to alter one or moreproperties, e.g., boiling point, of the precursor, e.g., to improve thecompatibility or reduce the incompatibility between the precursors.

As set forth above, the reaction zone gas phase constituents aretypically adjusted to provide a reducing environment within the reactionzone, such as preferably with hydrogen. Further, the reducing conditionscan be further enhanced at the tail end of the zone prior to the metalnon-oxide coated particle substrates undergoing reaction quench atsignificantly lower temperatures. The use of the combination of stagedreduction zones within the reaction zone and tail portion of thereaction zone can be particularly beneficial for creating optimumproperties, particularly film uniformity and morphology.

In addition to stage reduction, the anion forming precursor when in theform of a gas can be staged for optimizing the contact efficiency withthe metal non-oxide precursor coated powder substrate in the reactionzone. Further, the gaseous constituents in the reaction zoneparticularly under reducing conditions should be present at aconcentration that enhances reduction of oxide type metal non-oxideprecursors and/or contaminant oxygen that might enter the reaction zone.As set forth above, the metal non-oxide coating on the substrate shouldnot have substantially deleterious contaminants such as the deleteriouspresence of contaminant amounts of metals and contaminant oxygen anion.

The liquid compositions, which include non-oxide precursor, can alsoinclude the anion forming precursor. In this embodiment, the anionforming precursor can be soluble and/or dispersed homogeneously and/oratomizeable as part of the reactant mixture. Such mixtures areparticularly effective since the amount of anion forming precursor inthe final metal non-oxide coating can be controlled by controlling theconcentration of anion forming precursor in the reactant mixture. Inaddition, both the non-oxide precursor and anion forming precursor areassociated with the substrate in one step.

The substrate preferably is composed of at least a part of any suitableinorganic material and may be in any suitable form. By the term suitableinorganic substrate is meant that the majority of the external surfaceof the particle substrate be inorganic, more preferably greater thanabout 75% and still more preferably greater than about 95% of thesurface being inorganic. The internal core of the particle substratescan be organic, preferably organic polymers having high temperaturethermal stability under the fast reaction temperature conditions in thereaction zone. The polymers can be thermoplastics or thermosets,preferably high temperature thermoplastics such as polyimides,polyamide-imides, polyetherimides, bismalemides, fluoroplastics such aspolytetrafluoroethylene, ketone-based resins, polyphenylene sulfide,polybenzimidazole, aromatic polyesters, and liquid crystal polymers.Most preferred are imidized aromatic polyimide polymers,para-oxybenzoylhomopolyester and poly(para-oxybenzoylmethyl) ester. Inaddition polyolefines, particularly crystalline high molecular weighttypes can be used. The preferred organic substrates are high temperaturestable substrates, preferably inorganic organic substrates prepared byprecoating the organic substrate with an inorganic precoat as set forthbelow.

Preferably, the substrate is such so as to minimize or substantiallyeliminate deleterious substrate, coating reactions and/or the migrationof ions and other species, if any, from the substrate to the metalnon-oxide-containing coating which are deleterious to the functioning orperformance of the coated substrate in a particular application.However, a controlled substrate reaction which provides the requisitestoichiometry can be used and such process is within the scope of thisinvention. In addition, the substrate can be precoated to minimize ionmigration, for example an alumina and/or a silica including a silicateprecoat and/or to improve wetability and uniform distribution of thecoating materials on the substrate and/or to provide a surface forreaction with the anion forming precursor. The precoats can comprise oneor more members of a group of alumina, zirconium, silica, tungsten andtitanium oxides and other oxide halides and organooxy halides. Theprecoats can be deposited on the substrates including inorganic andorganic core substrates using any suitable technique such as hydrolysisand precipitation of a soluble salt. Further, as set forth above, theprecoats can be deposited on the substrates using such techniques asspray coating, dip coating followed by drying such as spray drying. Inaddition, the precoat process can be repeated in order to obtain aprecoat thickness to for example minimize deleterious effects fromcations contained in the substrate and/or improve the thermal barrierproperties of the precoat in relationship to an organic core and/or toprovide the desired metal non-oxide coating thickness.

In addition to the above techniques for forming a precoat, the substrateparticles, particularly the inorganic particles, can be processed inaccordance with the process of this invention with a precoat formingmaterial such as silicic acid or disilicic acid. In general, the precoatprecursor would be combined with the substrate to form a precoatreaction mixture which is then subjected to process conditions in thereaction zone in order to obtain reaction of the precursor precoatcomponent on the substrate. It is contemplated within the scope of thisinvention that a single or multi step process can be used, i.e. thefirst stage of a multistage being a precoat of the substrate in thereaction zone using the various types of feeds similar to those setforth above which contain the precoat precursor and subjecting such feedto fast reaction elevated temperature conditions in a reaction zone toform the precoated substrate. The precoated substrate can be combinedwith the metal non-oxide precursor to be further processed according tothe process of this invention.

It has also been found that the substrate itself can be selectivelyreacted and/or melted at the surface to produce a reactive surfaceand/or a precoat barrier layer, preferably a melt/resolidification/metalnon-oxide coating, still more preferably a majority or even greatercrystalline layer on the outer surface of the inorganic substrate. Theselective reaction and/or melting of the surface of the inorganicsubstrate can provide both the metal non-oxide coating and barrierproperties as well as enhanced bondability of the metal non-oxidecoating on the substrate, particularly with the formation of crystallinetype surface coating as set forth above. The process for the selectivereaction and/or melting of the surface of the inorganic substrate can bedone in multiple process steps or in a single step in carrying out theprocess of this invention. For example, the selective melting of theexternal surface of the inorganic substrate can be done in a mannersimilar to the formation of a reactive and/or barrier coating as setforth above followed by incorporating the surface modified substratealong with the anion forming precursor to form the reactant mixture. Thereaction mixture is then processed according to the process of thisinvention. In addition the reactant mixture can be introduced into thereaction zone under conditions wherein the selective reaction and/ormelting and resolidification of the surface of the inorganic substratetakes place, i.e. a single step process in the presence of an anionforming precursor. It has been found that the inorganic substrate havinga surface that has undergone selective reaction and/or melting,resolidification has unique properties with the inner core associatedwith the metal non-oxide coating. These improved properties can includeenhanced coating and barrier properties, bonding of the inner core withthe metal non-oxide coating and overall morphology stability.

In order to provide for controlled conductivity and/or absorption ofmetal non-oxide coatings, it is preferred that the substrate and/orinner core be substantially nonconductive and/or non-deleterious furtherreactive and/or substantially non-absorbing when the coated substrate isto be used as a component/such as additive in an electronic device,packaging device and/or film device. The substrate can be partially orcompletely inorganic, for example mineral, glass, ceramic and/or carbon.Examples of three dimensional substrates which can be coated using thepresent process include spheres, extrudates, flakes, fibers, aggregates,porous substrates, stars, irregularly shaped particles, tubes, such ashaving an average largest dimension of from about 0.05 microns to about250 microns, more preferably from about 1 micron to about 75 microns.

A particularly unique embodiment of the present metal non-oxide coatedparticles is the ability to design a particular density for a substratethrough the use of one or more open or closed cells, including micro andmacro pores particularly, including cell voids in spheres which spheresare hereinafter referred to as hollow spheres. Thus such densities canbe designed to be compatible and synergistic with other components usedin a given application, particularly optimized for compatibility inliquid systems such as polymer film coating and composite compositions.The average particle density can vary over a wide range such asdensities of from about 0.1 g/cc to about 2.00 g/cc, more preferablyfrom about 0.13 g/cc to about 1.5 g/cc, and still more preferably fromabout 0.15 g/cc to about 0.80 g/cc.

A further unique embodiment of the present invention is the ability toselectively have a metal non-oxide coating on the outer surface areawhile limiting the metal non-oxide coating on the internal pore surfacearea of the substrate typically limiting the coating to at least about10% noncoated internal pore surface area as a percentage of the totalsurface area of the substrate. Typically, the porous substrates willhave a total surface area in the range of from about 0.01 to about 700m²/gram of substrate, more typically from about 1 to about 100 m²/gramof substrate. Depending on the application such as for catalysts, thesurface area may vary from about 10 to about 600 m²/gram of substrate.

As set forth above, porous powder substrate particles can be in manyforms and shapes, especially shapes which are not flat surfaces, i.e.,non line-of-site materials such as pellets, fiber like, beads, includingspheres, flakes, aggregates, and the like. The percent apparentporosity, i.e., the volume of open pores expressed as a percentage ofthe external volume can vary over a wide range and in general, can varyfrom about 20% to about 92%, more preferably, from about 40% to about90%. A particularly unique porous substrate is diatomite, a sedimentaryrock composed of skeletal remains of single cell aquatic plants calleddiatoms typically comprising a major amount of silica. Diatoms areunicellular plants of microscopic size. There are many varieties thatlive in both fresh water and salt water. The diatom extracts amorphoussilica from the water building for itself what amounts to a strong shellwith highly symmetrical perforations. Typically the cell walls exhibitlacework patterns of chambers and partitions, plates and apertures ofgreat variety and complexity offering a wide selection of shapes. Sincethe total thickness of the cell wall is in the micron range, it resultsin an internal structure that is highly porous on a microscopic scale.

Further, the actual solid portion of the substrate occupies only fromabout 10-30% of the apparent volume leaving a highly porous material foraccess to liquid. The mean pore size diameter can vary over a wide rangeand includes macroporosity of from about 0.075 microns to 10 micronswith typical micron size ranges being from about 0.5 microns to about7.5 microns. As set forth above, the diatomite is generally amorphousand can develop crystalline character during calcination treatment ofthe diatomite. For purposes of this invention, diatomite as produced orafter subject to treatment such as calcination are included within theterm diatomite.

The particularly preferred macroporous particles for use in thisinvention are diatomites obtained from fresh water and which havefiber-like type geometry. By the term fiber-like type geometry is meantthat the length of the diatomite is greater than the diameter of thediatomite and in view appears to be generally cylindrical and/orfiber-like. It has been found that these fiber-like fresh waterdiatomites provide improved properties in coatings and compositeapplications.

As set forth above, substrates can be inorganic for example, carbonincluding graphite and/or an inorganic oxide. Typical examples ofinorganic oxides which are useful as substrates include for example,substrates containing one or more silicate, aluminosilicate, silicaparticularly high purity silica, sodium borosilicate, insoluble glass,soda lime glass, soda lime borosilicate glass, silica alumina, titaniumdioxide, mica, as well other such glasses, ceramics and minerals whichare modified with, for example, another oxide such as titanium dioxideand/or small amounts of iron oxide.

Additional examples of substrates are wollastonite, titanates, such aspotassium hexa and octa titanate, carbonates and sulfates of calcium andbarium; borates such as boric oxide, boric acid and aluminum borate, anatural occurring quartz and various inorganic silicates, clays,pyrophyllite and other related silicates.

A particularly unique metal non-oxide coated three-dimensional substrateis a flake and/or fiber particle, such as having an average largestdimension, i.e. length of from about 0.1 micron to about 200 micronsmore preferably from about 1 micron to about 100 microns, and still morepreferably from about 5 microns to about 75 microns, particularlywherein the aspect ratio, i.e., the average particle length divided bythe thickness of the particle is from about five to one to about 200 to1, more preferably from about 25 to 1 to about 200 to 1 and still morepreferably, from about 50 to 1 to about 200 to 1. Generally, theparticles will have a thickness varying from about 0.1 microns to about15 microns, more preferably from about 0.1 micron to about 10 microns.The average length, i.e., the average of the average length plus averagewidth of the particle, i.e., flake, will generally be within the aspectratios as set forth above for a given thickness. Thus for example theaverage length as defined above can vary from about 1 micron to about300 microns, more typically from about 20 microns to about 150 microns.In general, the average length can vary according to the type ofsubstrate and the method used to produce the platelet material. Forexample, C glass in general has an average length which can vary fromabout 20 microns up to about 300 microns, typical thicknesses of fromabout 1.5 to about 15 microns. Other particle materials for example,hydrous aluminum silicate mica, in general can vary in length from about5 to about 100 microns at typical thicknesses or from about 0.1 to about7.0 microns, preferably within the aspect ratios set forth above. Inpractice the particles which are preferred for use in such applicationsin general have an average length less than about 300 microns and anaverage thickness of from about 0.1 to about 15 microns. Ceramic fibersare particularly useful substrates.

A particular unique advance in new products resulting from the processof this invention are the production of metal non-oxide coated nanoparticle substrates typically having an average particle size less than3,000 nanometers, typically less than 2000 and still typically less than1000 nanometers. In many applications the average particle size will beless than about 200 nanometers. The particle size distribution of thenano particle substrates are skewed towards the smaller particle sizeand typically have greater than 90%, often greater than 95% of the totalnumber particles on a weight basis, less than 3,000 nanometers,typically less than 2000 nanometers, and still more typically less than1000 nanometers. It has been discovered that the use of liquid slurryreaction mixtures particularly metal non-oxide precursor which aresoluble in the slurry liquid are able to produce metal non-oxide coatednanosubstrates which vary in thickness from about 2% to about 75%, morepreferably from about 5% to about 60% of the average thickness on thesmallest dimension of the substrate particle, such as the thickness in aflake or the diameter in a fiber. The various physical and chemicalproperties of the substrates and coatings as set forth above areapplicable to nanosubstrates. The significant advantage of the solublemetal non-oxide precursor is the ability to provide the concentration ofthese coating forming components that produce the desired coatingthickness on the nanosubstrates.

A particular unique substrate is referred to as swelling clays orsmectites. These types of clays have a layered structure where in eachlayer can be treated to expand the spacing between layers such as toprovide individual layers of the clay of vary small thicknesses such asfrom about 1 to 2 nanometers. The aspect ratios are significantparticularly if the largest length extends to 1,000 nanometers. Thespacing between the different sheets are called the gallery which areexpanded upon treatment particularly with polar materials to provide forincreased spacing between each sheet.

These phyllosilicates, such as smectite clays, e.g., sodiummontmorillonite and calcium montmorillonite, can be treated with polarmolecules, such as ammonium ions, to intercalate the molecules betweenadjacent, planar silicate layers, for intercalation of precursor betweenthe layers, thereby substantially increasing the interlayer(interlaminar) spacing between the adjacent silicate layers. Thethus-treated, interclalted phyllosilicates, having interlayer spacingsof at least about 10-20. ANG. and up to about 100 ANG., then can beexfoliated, e.g., the silicate layers are separated, e.g., mechanically,by high shear mixing. The individual layers have been found tosubstantially improve one or more properties of polymer coatings andcomposites, such as mechanical strength and/or high temperaturecharacteristics.

Useful swellable layered materials include phyllosilicates, such assmectite clay minerals, e.g., montmorillonite, particularly sodiummontmorillonite; magnesium montmorillonite and/or calciummontmorillonite; nontronite; beidellite; volkonskoite; hectorite;saponite; sauconite; sobockite; stevensite; svinfordite; vermiculite;and the like. Other useful layered materials include micaceous minerals,such as illite and mixed layered illite/smectite minerals, such asrectorite, tarosiovite, ledikite and admixtures of illites with the clayminerals set forth above.

As set forth above the reaction mixture can be in a flowable powder formwith the metal non-oxide precursor present on the surface of thesubstrate as has been illustrated above. The metal non-oxide precursorcan be associated with the surface of the substrate by attractionthrough opposite static charges. In addition a binder can be associatedwith the metal non-oxide precursor, which enhances the association ofthe precursor with the substrate. The binder can be inorganic ororganic. As set forth above, the binder should not introduce anysubstantial deleterious contaminants into the metal non-oxide coating orsubstantially adversely affect the overall film properties such asconductive or absorption properties. The binders can be for examplepolymeric type such as polyvinylalcohol or polyvinylpyrrolidone. Inaddition, the binder can have both organic and inorganic functionalitysuch as an organic silicate such as an ethyl silicate. In addition, theinorganic binders can be used such as calcium silicate, boric oxide andcertain carbonate, nitrates and oxalates. In the case of organic bindersit is preferred to use such organic binders that will be converted to acarbon oxide such as carbon monoxide or carbon dioxide under the processconditions in the reaction zone without leaving any substantialdeleterious carbon or oxygen contaminant associated with the metalnon-oxide coated substrate. In addition, the use of organic binders canprovide for a reducing atmosphere in the reactor zone or the exit of thereactor zone. It is preferred to use a binderless flowable powderreaction mixture in order to eliminate potential contaminant effects.When a binder is used, the concentration of the binder is such as tomaintain the individual particle substrate integrity or if agglomerationdoes occur, to be easily converted to nonagglomerated particles throughlow severity mechanical processing such as ball milling.

The coated particles are particularly useful in a number ofapplications, particularly conductivity and absorption type applicationssuch as catalysts, thermal dissipation elements, electrostaticdissipation elements, electromagnetic interference shielding elements,electrostatic bleed elements, protective coatings and the like. Inpractice spherical particles for use in applications in general have aroundness associated with such particles, generally greater than about70% still more preferably, greater than about 85% and still morepreferably, greater than about 95%. The spherical products offerparticular advantages in many of such applications disclosed herein,including enhanced dispersion and rheology, particularly in variouscompositions such as polymer compositions, coating compositions, variousother liquid and solid type compositions and systems for producingvarious products such as coatings and polymer composites. Typicalexamples of products are boron nitride, silicon carbide and nitride,iron silicide, titanium carbide, boride and silicide, aluminum nitrideand molybdenum silicide

Any suitable matrix material or materials may be used in a compositewith the metal non-oxide coated substrate. Preferably, the matrixmaterial comprises a polymeric material, e.g., one or more syntheticpolymers, more preferably an organic polymeric material. The polymericmaterial may be either a thermoplastic material or a thermoset material.Among the thermoplastics useful in the present invention are thepolyolefins, such as polyethylene, polypropylene, polymethylpentene andmixtures thereof; and poly vinyl polymers, such as polystyrene,polyvinylidene difluoride, combinations of polyphenylene non-oxide andpolystyrene, and mixtures thereof. Among the thermoset polymers usefulfor powders of the present invention are epoxies, phenol-formaldehydepolymers, polyesters, polyvinyl esters, polyurethanes,melamine-formaldehyde polymers, and urea-formaldehyde polymers.

In addition, a thermal and/or electrostatic dissipation/electromagneticinterference shielding element is provided which comprises a threedimensional substrate, e.g., an inorganic substrate, having a conductivemetal non-oxide-containing coating on at least a portion of all threedimensions thereof. The coated substrate is adapted and structured toprovide at least one of the following: thermal and/or electrostaticdissipation and/or bleed and electromagnetic interference shielding.

A very useful application for the products of this invention is forstatic, for example, electrostatic, dissipation and shielding,particularly for polymeric parts, and more particularly as a means foreffecting static dissipation including controlled static discharge anddissipation such as used in certain electro static painting processesand/or electric field absorption in parts, such as parts made ofpolymers and the like, as described herein. Certain of the presentproducts can be incorporated directly into the polymer or a carrier suchas a cured or uncured polymer based carrier or other liquid, as forexample in the form of a liquid, paste, hot melt, film and the like.These product/carrier based materials can be directly applied to partsto be treated to improve overall performance effectiveness. A heatingcycle is generally used to provide for product bonding to the parts. Aparticularly unexpected advantage is the improved mechanical properties,especially compared to metallic additives which may compromisemechanical properties. In addition, the products of this invention canbe used in molding processes to allow for enhanced static dissipationand/or shielding properties of polymeric resins relative to an articleor device or part without such product or products, and/or to have apreferential distribution of the product or products at the surface ofthe part for greater volume effectiveness within the part.

The particular form of the products, i.e., fibers, flakes, irregularlyshaped and/or porous particles, or the like, is chosen based upon theparticular requirements of the part and its application, with one ormore of flakes, fibers and particles, including spheres, being preferredfor polymeric parts. In general, it is preferred that the products ofthe invention have a largest dimension, for example, the length of fiberor particle or side of a flake, of less than about 300 microns, morepreferably less than about 150 microns and still more preferably lessthan about 100 microns. It is preferred that the ratio of the longestdimension, for example, length, side or diameter, to the shortestdimension of the products of the present invention be in the range ofabout 500 to 1 to about 10 to 1, more preferably about 250 to 1 to about25 to 1. The concentration of such product or products in theproduct/carrier and/or mix is preferably less than about 60 weight %,more preferably less than about 40 weight %, and still more preferablyless than about 20 weight %. A particularly useful concentration is thatwhich provides the desired performance while minimizing theconcentration of product in the final article, device or part.

The products of this invention find particular advantage in staticdissipation parts, for example, parts having a surface resistivity inthe range of about 10⁴ ohms/square to about 10¹² ohms/square. Inaddition, those parts generally requiring shielding to a surfaceresistivity in the range of about 1 ohm/square to about 10⁵ ohms/squareand higher find a significant advantage for the above products due totheir mechanical properties. A further advantage for certain of theabove products is their ability to provide static dissipation and/orshielding in adverse environments such as in corrosive water and/orelectro galvanic environments. As noted above, certain products have theability to absorb electro fields. The unique ability of the products toabsorb allows parts to be designed which can minimize the amount ofreflected electro fields that is given off by the part. This latterproperty is particularly important where the reflected fields canadversely affect performance of the part.

The following examples illustrate the processes of this invention.

EXAMPLE 1

A flowable powder reaction mixture is formed from a high purity silicaplatelet having an average particle size of about 50 microns andtitanium tetrachloride by liquid film formation using ultrasonic dropletformation.

The reaction mixture is fed into a reaction zone as a nitrogen gasfluidized flowable powder at elevated temperature. The elevatedtemperature of 2700° K. is maintained by an RF induction plasma systemoperating at a power of about 30 kW at a frequency of 3 MHz. The centralswirl gas is argon and the sheath gas, a mixture of argon and hydrogen.The anion forming precursor carrier gas is nitrogen. The reactionmixture is introduced into the reaction zone at a flow rate of 7.5 gramsper minute. The gas velocities in the reaction zone are controlled toallow for an average particle residence time of about 15 milliseconds.The temperature within the reaction zone is controlled to allow for thestructural solid maintenance of the substrate. The introduction of thereaction mixture is assisted by the gas atomization of the reactionmixture. A titanium nitride coated silica powder substrate is recoveredin a collection zone. The collection zone uses a fabric bag filter toremove and recover the metal non-oxide coated substrates.

EXAMPLE 2

Example 1 is repeated except that methane is used as the anion formingprecursor and carrier gas. A titanium carbide coated silica substrate isrecovered in the collection chamber.

EXAMPLE 3

Example 1 is repeated except that a reducing flame combustion thermalsource is used in place of the RF induction plasma system. In place ofthe central, sheath and carrier gases, a combustion gas having minimummole % oxygen is generated using nitrogen diluted air and ammonia. Theaverage particle substrate residence time in the reaction zone was 15milliseconds. A titanium nitride coated silica substrate is recovered.

EXAMPLE 4

Example 1 is repeated except that the reaction mixture is a free flowingpowder obtained from contacting the silica platelet substrate withanhydrous aluminum chloride. The central gas is argon and nitrogenvapor, the sheath gas is hydrogen and argon and the carrier gas isnitrogen. The reaction mixture is introduced at a rate of about 6 gramsper minute. The average velocity of the particle substrate is 5 metersper second. An aluminum nitride silica platelet is recovered.

EXAMPLE 5

Example 4 is repeated except that the aluminum chloride is replaced byzirconium oxychloride. A zirconium nitride coating on the silicasubstrate is recovered in the collection zone.

EXAMPLE 6

Example 2 is repeated except that the substrate is mica and the mica isprecoated with diethyl chlorosilane silica precursor in place oftitanium chloride to form a reactive coating. The average particle sizeof the mica is 20 microns. A silicon carbide coated mica is recovered inthe collection zone.

EXAMPLE 7

Example 6 is repeated except the mica is replaced with a polyimidepowder having an average particle size of 40 microns. The silaneprecursor is diethyl chlorosilane. A silicon carbide coated polyimidesubstrate is recovered.

EXAMPLES 8 and 9

Examples 1 and 2 are repeated except the average particle substrateresidence time is increased to 30 milliseconds. A product having auniform crystalline coating on the silica substrate is recovered in thecollection zone.

While this invention has been described with respect to various specificexamples and embodiments, it is to be understood that the invention isnot limited thereto and that it can be variously practiced within thescope of the following claims.

What is claimed is:
 1. An article comprising a thermally associated nondeleterious contaminated metal non-oxide coated three dimensional powder particle substrate produced by the process comprising: forming a reactant mixture comprising a powder particle substrate, a metal non-oxide precursor and an anion forming precursor said metal of the metal non-oxide coating being formed from a metal non-oxide precursor substantially uniformly preassociated with at least a part of the external surface of the powder particle substrate prior to the coating being formed and associated and said metal and the anion of said precursors being chemically different, reacting said reaction mixture at thermal conditions in a reaction zone effective to form and associate a metal non-oxide coating on at least a portion of the external surfaces of said powder substrate at said thermal conditions without essentially chemically altering substrate; said thermal conditions in said zone including an average particle residence time of less than about one second when at thermal conditions.
 2. The article of claim 1 wherein the residence time is less than about 0.5 seconds and greater than about 1 millisecond.
 3. The article of claim 2 wherein the residence time is less than about 0.25 seconds and greater than about 1 millisecond.
 4. The article of claim 1 wherein the metal of the metal non-oxide precursor is selected from the group consisting of iron, titanium, boron, silicon, aluminum, molybdenum, zirconium, tungsten, nickel and mixtures thereof.
 5. The article of claim 4 wherein the metal is selected from the group consisting of titanium, boron, aluminum and silicon.
 6. The article of claim 1 wherein the anion forming precursor is a precursor for an anion selected from the group consisting of carbide, boride, sulfide, silicide, and nitride.
 7. The article of claim 6 wherein the anion is selected from the group consisting of nitride, boride and carbide and the powder particle is selected from the group consisting of a fiber, a flake, an irregularly shaped particle and mixtures thereof.
 8. An article comprising a thermally associated nondeleterious contaminated metal carbide coated three dimensional powder particle substrate comprising: forming a reactant mixture comprising a powder particle substrate, a metal carbide precursor and a carbide anion forming precursor said metal of the metal carbide coating being formed from a metal carbide precursor substantially uniformly preassociated with at least a part of the external surface of the powder particle substrate prior to the coating being formed and associated and said metal and the anion of said precursors being chemically different, reacting said reaction mixture at thermal conditions in a reaction zone effective to form and associate a metal carbide coating on at least a portion of the external surfaces of said powder substrate at said thermal conditions without essentially chemically altering the substrate; said thermal conditions in said zone including an average particle residence time of less than about one second when at thermal conditions.
 9. The article of claim 8 wherein the residence time is less than about 0.5 seconds and greater than about 1 millisecond.
 10. The article of claim 9 wherein the residence time is less than about 0.25 seconds and greater than about 1 millisecond.
 11. The article of claim 8 wherein the metal of the metal carbide precursor is selected from the group consisting of iron, titanium, boron, silicon, aluminum, molybdenum, zirconium, tungsten, nickel and mixtures thereof.
 12. The article of claim 11 wherein the metal is selected from the group consisting of titanium, boron, aluminum and silicon and the powder particle is selected from the group consisting of a fiber, a flake, an irregularly shaped particle and mixtures thereof.
 13. The article of claim 8 wherein the carbide forming precursor is selected from the group consisting of gaseous hydrocarbons, gaseous chloro hydrocarbons and powdered carbon.
 14. The article of claim 13 wherein the carbide forming precursor is selected from the group consisting of methane and powdered carbon.
 15. An article comprising a thermally associated nondeleterious contaminated metal nitride coated three dimensional powder particle substrate produced by the process comprising: forming a reactant mixture comprising a powder particle substrate, a metal nitride precursor and a nitride anion forming precursor said metal of the metal nitride coating being formed from a metal nitride precursor substantially uniformly preassociated with at least a part of the external surface of the powder particle substrate prior to the coating being formed and associated and said metal and the anion of said precursors being chemically different, reacting said reaction mixture at thermal conditions in a reaction zone effective to form and associate a metal nitride coating on at least a portion of the external surfaces of said powder substrate at said thermal conditions without essentially chemically altering the substrate and contributing deleterious oxide contaminants; said thermal conditions in said zone including an average particle residence time of less than about one second when at thermal conditions.
 16. The article of claim 15 wherein the residence time is less than about 0.5 seconds and greater than about 1 millisecond.
 17. The article of claim 15 wherein the metal of the metal nitride precursor is selected from the group consisting of iron, titanium, boron, silicon, aluminum, molybdenum, zirconium, tungsten, nickel and mixtures thereof.
 18. The article of claim 17 wherein the metal is selected from the group consisting of titanium, boron, aluminum and silicon and the powder particle is selected from the group consisting of a fiber, a flake, an irregularly shaped particle and mixtures thereof.
 19. The article of claim 15 wherein the nitride forming precursor is selected from the group consisting of nitrogen, ammonia and mixtures thereof.
 20. The article of claim 19 wherein the nitride forming precursor is nitrogen. 